This project will evaluate computed transmission tomography (CTT) as a method for imaging acute myocardial infarcts. The first phase will utilize radioisotope microspheres to investigate the role of coronary collaterals in producing the phenomenon of delayed contrast enhancement of infarcts in dogs. The second phase will test the sensitivity of CTT for detecting infarction in humans and determine its accuracy for quantifying infarct size. In addition, perioperative infarction associated with coronary bypass surgery will be studied to determine if the associated early reperfusion produces image differences when compared to natually occurring infarcts. During the project's final phase a new ultrafast CTT scanner (CVCT) will be evaluated for imaging infarcts in animals and humans. The CVCT's 30-50 msec scan speed and multiple simultaneous slice capability will mkae measurement of regional myocardial blood flow possible. The technique will be validated by radioisotope microsphere studies in dogs. With increasing use of drugs such as streptokinase to limit infarct size, the need for an accurate method for quantifying infarct size is greater than ever. Contrast enhanced CTT offers real promise for fulfilling this need.